Conventionally, a structure as shown in FIG. 8 is known as a solid electrolytic capacitor (8). The solid electrolytic capacitor includes a capacitor element (15) in which a dielectric oxidized film (2), a solid electrolytic layer (3), and a cathode lead layer (4) made of carbon or silver, for example, are formed in that order on a surface of an anode member (1), which is made of a sintered valve metal (tantalum, niobium, titanium, or aluminum, for example). The solid electrolytic layer (3) is made of conductive inorganic material such as manganese dioxide, or conductive organic material such as TCNQ complex salt or conductive polymer. A bar-shaped or plate-shaped anode lead (16) protrudes from one end of the anode member (1). It is possible to feed a great amount of current through the plate-shaped anode lead (16), as disclosed in JP 2000-12387A.
An anode lead frame (20) is fastened to this anode lead (16) by resistance welding or the like, and a cathode lead frame (21) is fastened to the cathode lead layer (4) by a conductive adhesive (5). The lead frames (20) and (21) are the boards made of copper or an alloy whose principal component is copper (see JP S63-293147A), in view of conductivity and thermal conductivity. It is possible to make the internal resistance of the capacitor small if the conductivity of the lead frames (20) and (21) is high. A housing (7) made of epoxy resin, for example, covers the outside of the capacitor element (15).
However the above-described capacitor has the following problem: The lead frames (20) and (21) are made of a material with high conductivity and high thermal conductivity. Therefore, when fastening the anode lead (16) by resistance welding, the generated joule heat and the applied current are conducted from the locations to be welded to other locations. As a result, welding strength of the resistance welding is not consistent and the anode lead (16) is easily detached from the anode lead frame (20).